A number of methods are already known in which prereduced ore is melted down together with coal and the resulting gas utilized to reduce fresh iron ore.
The process according to German "offenlegungsschrift" No. 31 33 75 improves the heat supply in the melt-down vessel by having reaction gases from the iron melt sucked in in the space above the melt by oxygen blown onto the bath surface, with the reactor gases carried along to the bath surface and partly burned, with the resulting heat transferred to the iron melt. In this known method liquid iron is produced by the addition of ore to the iron bath reactor. The carbonaceous gas formed at the same time can be used to prereduce ore. However, the fuel consumption in this method is relatively high.
The process according to German Pat. No. 28 43 303 involves the same disadvantage. In this process lumpy coal is fed to a fluidized bed located on the iron bath and the gases serve to prereduce iron ore. To produce 1 t of liquid iron from the ore prereduced in the gaseous phase to a high degree of metallization, approximately 900 kg of high-quality coal is required. However, this process produces a considerable surplus of gas whose exploitability essentially determines the economy of the process.
German "offenlegungsschrift" 34 18 085 describes a method for producing iron from ore, in which the ore is reduced in an ore reduction vessel to a metallization degree of approximately 50% with the reaction gases from the melt-down vessel. In this process the reaction gases emerging from the iron melt are afterburned in the melt-down vessel by 30 to 40%, and the resulting heat is transferred to a large extent to the melt. The reaction gases are then reduced and at the same time cooled on the way from the melt-down vessel to the ore reduction vessel, by the addition of reducing agents such as natural gas or dust coal.
Another known method uses substantially prereduced iron ore with a metallization degree of 92 to 94%, which is melted down in the melt-down vessel together with carbonaceous, solid energy carriers and oxygen. The resulting gas serves to prereduce the ores and, to improve its utilization, the gas is circulated and the CO.sub.2 therein removed.
The latter two methods thus combine three steps to arrive at a minimum fuel consumption, i.e. the melt reduction with afterburning, hot gas reduction of the waste gases from the melt-down vessel, and prereduction of the ores in the gaseous phase, on the one hand, and melting down with coal and oxygen without afterburning, utilization of the gases for prereduction, and removal of the CO.sub.2 during the gas recycling, on the other hand. These processes require approximately 600 kg of coal to produce 1 t of iron from iron ore.